Motivation

This research is aimed at investigating the possibility that
large-scale anomalous heat source (e.g. heat wave event) might be
capable of triggering widespread turbulence in the space/ionospheric
plasma layer through the excitation of acoustic-gravity waves (AGWs). This hypothesis was motivated by the observation of intense traveling ionospheric disturbances (TIDs) over Arecibo Observatory,
Puerto Rico, for several consecutive days in the summer 2006. At that time, the geomagnetic condition was relatively quiet, and there were no major earthquake, tsunami, or volcanic eruptions. However,
we note that during this time period, a relatively severe and
prolonged heat wave was steadily sweeping eastward across the
mainland United States [1]. These findings therefore suggest that the thermal gradients associated with the heat wave fronts are
generating AGWs that could propagate through long distances to induce
space plasma turbulence in the form of TIDs over an extended region [2].

Through this work, we hope to better understand the behavior of space
plasma environment as the earth climate changes. This is especially intriguing because, according to some climate models, we could expect severe and prolonged heat waves to occur more frequently in a warmer earth climate [3].

Approach / Tools

We are employing two separate approaches to investigate this hypothesis:

- study the level of fluctuations in total electron content (TEC)
over the North American sector in response to heat wave events.
- physically simulate AGW/TID excitation by thermal gradients under
controlled conditions in a set of ionospheric HF heating experiments.

In the first approach (i.e. mapping of TEC fluctuations), we are
looking for possible correlation between the heat wave event and the
increase in the level of ionospheric plasma disturbance within the
area of interest. In the second approach (i.e. HF heating experiments), we aim to generate some artificial time-varying thermal
gradients directly at ionospheric heights and see if AGWs/TIDs are
being generated.

In this HF heating experiment, we utilize a number of ground-based
and satellite diagnostics (which include HF and UHF radars, as well
as GPS and LEO satellites). We aim to detect the plasma disturbances
generated by the modulated heating, and to be able to distinguish it
from natural ionospheric disturbances that might happen to pass
overhead during the experiments. Possible contamination from
naturally-occurring disturbances generally can be minimized by
conducting the experiments during geomagnetically quiet times.